A carbon nanotube is a crystalline carbon with a structure in which a thin layer of graphite crystal is rolled-up into the shape of a cylinder. In other words, carbon atoms of which a carbon nanotube is composed from a graphene structure, which is a flat or curved layer formed by arranging six-membered rings of carbon atoms in a honeycomb. A cylindrical structure in which such a layer is rolled-up in one direction is the carbon nanotube. In general, those with a diameter of several nanometers to several ten of nanometers and a length of several ten times to not less than several thousand times longer than its diameter are called “carbon nanotubes”. Carbon nanotubes are classified into single-walled carbon nanotubes formed by a single graphene layer rolled-up in the shape of a cylinder, which may be abbreviated to “SWCNT”, and multi-walled carbon nanotubes formed by two or more graphene layers rolled-up in the shape of a cylinder, which may be abbreviated to “MWCNT”. Furthermore, the single-walled carbon nanotubes take three types of shapes, which are “armchair”, “zigzag”, and “chiral”, depending on how the six-membered rings are arranged.
The multi-walled carbon nanotubes have physical properties of large electric conductivity, high elasticity, high strength, etc. On the other hand, the single-walled carbon nanotubes have a wide variety of unique properties, such as high elasticity, electric properties that enable the nanotubes to be used as conductors or semiconductors; mechanical properties including extreme strength, thermal conductivity larger than the thermal conductivity of diamond, and occlusion and absorption of molecules. See, for example, patent document 1. The single-walled carbon nanotubes also have a Young's modulus of several thousand GPa, a tensile strength of several ten GPa, which is measured in a scanning electronic microscope. The single-walled carbon nanotubes further have a property of being hardly broken, to such an extent that upon the receipt of a bending stress they further deform, having a wave-like structure on the side of being compressed. See, for example, non-patent document 2. Therefore, the single-walled carbon nanotubes with these properties are expected to be applicable to various technical fields, such as antistatic agents, conductive ink and paint, hydrogen occluding agents, semiconductors, chemical reactions, supports for fuel-cell catalysts, materials for the negative electrode of secondary batteries, sensors, devices, fillers for composite materials, space craft and aircraft technologies, and bio- and medical-technologies.
Carbon nanotubes are normally produced by various methods, such as arc-discharge methods, laser evaporation methods, thermal CVD methods, wherein CVD stands for “chemical vapor deposition”, and flowing vapor deposition methods. The arc-discharge method is a method of growing carbon nanotubes by means of arc discharge using carbon electrodes. The arc-discharge method is capable of producing an enormous amount of carbon nanotubes. The laser evaporation method typically forms carbon nanotubes by evaporating part of a graphite electrode by means of a laser. The thermal CVD method grows carbon nanotubes at a high temperature by thermally decomposing hydrocarbon, which is a carbon source, on a substrate with a metal catalyst thereon. The flowing vapor deposition method generates carbon nanotubes by making an organic transition metal compound and a hydrocarbon compound, which is a carbon source, both flowing with a carrier gas, react with each other at a high temperature. In addition to them, there are various methods such as a method of using a plasma chemical vapor deposition apparatus, a thermal chemical vapor deposition apparatus and the like, for example.
An example of more specific processes of producing carbon nanotubes is a process for producing carbon nanotubes at a high yield rate by arranging a carbon source polymer on a template and calcining it at a high temperature. See patent document 1. Another example is a chemical vapor deposition method capable of producing a great amount of carbon nanotubes. See patent document 2. Patent document 3 discloses a method of amorphous carbon nanotubes different from the above-mentioned carbon nanotubes. Patent document 4 teaches a method of producing carbon nanotubes by introducing an organic solvent solution that includes a catalyst metal compound, especially a salt of a catalyst metal dissolved in a solvent, into a heating oven at a temperature of 700° C. to 1500° C.
Carbon nanotubes can be produced by these methods. In order to apply single-walled carbon nanotubes with the aforementioned properties that multi-walled carbon nanotubes do not have to various technical fields, however, single-walled carbon nanotubes have to be produced with high purity. The problem associated with the above-mentioned methods is that they produce multi-walled carbon nanotubes, or a mixture of a major amount of multi-walled carbon nanotubes and a minor amount of single-walled carbon nanotubes. The production of single-walled carbon nanotubes is very difficult especially by the flowing vapor deposition method and the chemical vapor deposition method. Therefore in order to utilize single-walled carbon nanotubes in various technical fields, it is necessary to develop a method capable of specifically producing single-walled carbon nanotubes.    Patent document 1: JP-A-2003-146632    Patent document 2: JP-A-2001-81564    Patent document 3: JP-A-2002-293520    Patent document 4: JP-A-2003-221215    Non-patent document 1: Page 120 of “Basics and Applications of Carbon Nanotubes” written by Riichiro Saito et al., published on Mar. 31, 2004 by Baifukan Co., Ltd.    Non-patent document 2: Chapter 7, “Mechanical Strength of Carbon Nanotubes” of “Carbon Nanotubes” written by Kazuyoshi Tanaka, published on Jan. 30, 2001 by Kagaku-dojin Publishing Company, Inc.